A fuzzy set theory solution to combining Likert items into a single overall scale (or subscales)

Likert scales (or subscales) are usually constructed by summing up the items when the assessment of their psychometric properties has resulted in showing that the scale is both reliable and valid. This paper presents a methodology for developing a fuzzy set theory solution to combine Likert items into a single overall scale (or subscales). The proposed methodology puts together information produced by construct validity assessment, statistical analysis and experts’ knowledge produced during theory development, in a fuzzy inference system to develop a more accurate attitude measurement. The evaluation of the methodology presented is tested on a Likert scale that was used in a large-scale sample survey for measuring xenophobia in Northern Greece conducted by the National Centre for Social Research. The methodology can be applied with minor modifications to other data sets.